The present invention relates to a drive control system for sensor-less motor and more specifically to the technique which may effectively be applied to the drive control of a brush-less DC multi-phase motor not including a rotation detecting sensor, for example, the technique which can be effectively applied to the drive control of a spindle motor for high speed drive of a disk storage medium (platter) of a HDD (hard disk drive)
The HDD reads or writes information with the seeking and following operations of a magnetic head on a recording surface formed on the surface of platter while the disk type magnetic recording medium called the platter is rotated at a high speed. In order to realize high speed read/write operations of information in this HDD, the rotating speed of platter must be increased.
The platter is driven to rotate with a spindle motor. For this spindle motor, a sensor-less motor is generally used. This sensor-less motor is a brush-less DC multi-phase motor not including a rotation detecting sensor. This motor is suitable, for example, for high speed rotation of a disk type recording medium such as a platter.
The sensor-less motor can form an effective structure of the motor and drive system thereof since an independent rotation sensor is not used to detect the magnetic pole position of a rotor. Instead, the magnetic pole position of rotor must be detected without use of the sensor. Therefore, the magnetic pole position of rotor is detected, in the sensor-less motor of this type, by utilizing B-EMF (Back Electromagnetic Force) induced on a field coil. B-EMF is a voltage induced on the field coil through the rotation of a rotor. Therefore, when the rotor is in the rotating condition, the magnetic pole position of rotor and rotating speed can be detected by utilizing its B-EMF.
In the case where this sensor-less motor is used as the spindle motor, the motor is driven to rotate with an open loop control and is sequentially subjected to the commutation control and PLL (phase lock loop) control based on the back electromotive force of the field coil in view of holding the motor in the predetermined steady rotating speed condition. The sequence control up to the steady operation from this drive can be conducted with an LSI (semiconductor integrated circuit) system.